Question

Which of the following statements are correct with reference to packaging of DNA helix?
A. Histones are organized to form a unit of eight molecules called histone octamer.
B. Histones are negatively charged basic proteins.
C. Histones are rich in the basic amino acid residues – lysine and arginine.
D. The positively charged DNA is wrapped around the histone octamer to form nucleosome.
E. The packaging of chromatin at higher levels requires an additional set of proteins called non-histone chromosomal proteins. Choose the correct answer from the options given below :

• A. A, B and D only
• B. B, D and E only
• C. A, C and E only
• D. C, D and E only

Hint:

Remember: DNA is Decidedly Negative (due to phosphate groups). Histones are Highly positive basic proteins. Opposites attract to form the nucleosome!

Answer 1

The Correct Option is C

The packaging of DNA is a complex process that allows long DNA threads to fit into the microscopic nucleus. The evaluation of the statements is as follows:
• Statement A is Correct: Histones are indeed organized into a unit of eight molecules to form the histone octamer.
• Statement B is Incorrect: Histones are positively charged proteins, not negatively charged. Their basic nature and positive charge allow them to interact with the negatively charged DNA.
• Statement C is Correct: Histones acquire their charge because they are rich in basic amino acid residues like lysine and arginine, both of which carry positive charges in their side chains.
• Statement D is Incorrect: The statement is inverted. It is the negatively charged DNA that is wrapped around the positively charged histone octamer to form the nucleosome.
• Statement E is Correct: While nucleosomes represent the first level of packaging, further condensation of chromatin into chromosomes requires Non-Histone Chromosomal (NHC) proteins. Therefore, statements A, C, and E are the only correct ones.